A key to refinish coatings is the ability to deliver a refinished vehicle to the customer as quickly as possible with a maximum level of appearance. The consumer wants to have a good-looking, repaired vehicle as quickly as possible to minimize the inconvenience of being without a vehicle. The repair shop wants to maximize the utilization of his capital investment and minimize the overall labor and cost in repairing a vehicle. Thus, productivity in the overall repair process and good appearance is critical.
Additionally, pressures exist worldwide to develop low volatile organic compounds (“VOC”), that is, environmentally friendly coating systems. One key to resolving these issues is through the dramatic reduction or elimination of solvents used in coatings. These new, low VOC coatings need to meet key customer attributes including productivity, appearance, and film properties while being robust, user-friendly systems.
Currently, the automotive refinish market is comprised mostly of two-pack coating compositions having two components stored in separate containers capable of curing at ambient conditions into crosslinked, three-dimensional, thin films. These two-pack coating compositions are predominantly solvent based and use hydroxyl/isocyanate curing. One component of the two-pack coatings contains crosslinkable functional groups, such as hydroxyl groups; the other component contains crosslinking groups, such as isocyanate groups. The two components are mixed just prior to spraying on a substrate, such as a vehicle body. These two-pack coating compositions need to remain at a low enough viscosity to allow for spraying over an extended timeframe and then, after spraying, require rapid curing to a three-dimensional network on the substrate, such as a vehicle body to maximize productivity and physical properties.
In repairing damage such as a dent to a vehicle body, the original coating in and around the damage is typically sanded or ground out by mechanical means. Sometimes the original coating is stripped off from a portion or off the entire vehicle body to expose the bare metal underneath. After repairing the damage, the repaired surface is coated, preferably with low VOC coating compositions, typically in portable or permanent low cost painting enclosures vented to atmosphere to remove the organic solvents from the freshly applied paint coatings in a safe manner from the standpoint of operator health and explosion hazard. Typically, the drying and curing of the freshly applied paint coatings takes place within these enclosures. Furthermore, the foregoing drying and curing steps take place within the enclosure to prevent the wet paint coatings from collecting dirt in the air or other contaminants.
As these paint enclosures take up significant floor space of typical small vehicle body shops, these shops prefer to dry and cure these paint coatings as fast as possible. One way to accelerate drying and curing of the freshly applied paint coatings is to provide heat sources such as conventional heat lamps, infrared radiation heaters, or hot air to the enclosure. However, addition of the heat sources increases not only operational costs, but also the energy consumption of the shops and therefore is not desired by the small vehicle body shops. Therefore, to provide more cost and energy effective utilization of shop floor space and to minimize fire hazards resulting from wet coatings from solvent based coating compositions, there exists a continuing need for fast curing coating formulations that cure under ambient conditions while still providing outstanding performance characteristics, particularly chip resistance, mar-resistance, durability, and appearance.
A key aspect of the productivity in refinish coatings is the ability for physical dry. High productivity coatings need to be able to dry to the touch very rapidly to allow for application of subsequent coats.
A commonly owned, co-pending Published U.S. Patent Application No. 2005/0209433 discloses a coating composition wherein orthoester groups block the crosslinkable hydroxyl groups of the poly(meth)acrylate wherein the orthoester groups can be removed through hydrolysis to generate de-blocked crosslinkable hydroxyl groups. The de-blocked crosslinkable hydroxyl groups then react with crosslinking compounds having isocyanate crosslinking groups. Published U.S. Patent Application No. 2005/0209433 further discloses a process for coating substrates wherein a clearcoat comprising the aforementioned coating composition is coated over a basecoat. A process for blocking the hydroxyl groups of a poly(meth)acrylate compound through reaction with an orthoester compound is also disclosed.
Published U.S. Patent Application No. 2005/0165199 discloses a process for preparing polymers containing polyortho ester groups and optionally isocyanate groups by reacting A) and B) where A) is a polyortho ester containing at least one isocyanate-reactive crosslinkable group prepared by reacting at least one or more acyclic orthoesters with low molecular weight polyols having a functionality of 4-8 and a number-average molecular weight of 80-500 g/mol and B) is at least one polyisocyanate having at least one crosslinking isocyanate group. The polymers obtained from the process can be used to produce coating compositions, adhesives and/or sealers. The coating compositions can include one or more of the above-described polymers, optionally polyisocyanates, catalysts, and optionally auxiliaries and additives.
It is desirable to improve physical dry and long pot life through the use of novel polyols with protected hydroxyl groups. The coatings disclosed herein are stable under anhydrous conditions but become active, or de-blocked, after being applied to a substrate and exposed to atmosphere, wherein the absorption of atmospheric moisture will de-block the hydroxyl groups. The de-blocked hydroxyl groups then quickly react with the isocyanate crosslinking groups in the coating composition to develop a three-dimensional network, and very rapid film formation occurs.